1. Field of the Invention
Embodiments of the present invention generally relate to lithography and to electron (or other energy) beam columns, and more specifically to a writing technique using variable shaped beams.
2. Description of the Related Art
It is well known in the field of lithography (pattern generation) that it is desirable to increase the accuracy of pattern generation systems. Two main applications for such pattern generation systems are making masks for use in semiconductor fabrication by electron beam lithography and electron beam direct writing of patterns onto wafers to form semiconductor devices.
Lithography systems generate or expose patterns by controlling the flow of energy (the beam) from a source to a substrate coated with a layer sensitive to that form of energy. Pattern exposure is controlled and broken into discrete units commonly referred to as flashes, wherein a flash is that portion of the pattern exposed during one cycle of an exposure sequence. Flashes are produced by allowing energy from the source, for example light, electron or other particle beams, to reach the coated substrate within selected pattern areas. The details of flash composition, dose and exposure sequence used to produce a pattern, and hence the control of the lithographic system, are generally known as a writing strategy.
Often times, however, the beam and/or the apertures used in connection with generating the beam may drift over time and move due to noise, thereby negatively affecting critical dimension uniformity of the figures associated with the pattern. Such negative effects may commonly be referred to as critical dimension uniformity errors. Such errors may be caused by a number of factors, such as shaping electronic noise, noise due to aperture and column mechanical vibrations, beam noise due to magnetic field radiation, beam drift, random errors in the electron dose and vector electronics noise.
Since slowly varying noise and drift are often related to environmental conditions that are only partially under control, a need exists in the art for a method and system for a writing strategy that mitigates critical dimension uniformity errors caused by the drifts and low frequency noises.